#include #ifndef __DATE__ #error wait a second... #define ERROR #endif #ifndef ERROR #define PI 3.14159 #define max(a,b) ((a)>(b)?(a):(b)) #define square1(x) x*x #define square2(x) ((x)*(x)) int main() { std::cout << "We are going to learn how to use the #define command of preprocessor" << std::endl << std::endl; std::cout << "First of all we can use the #define to create constant with this syntax : \"#define name_of_the_variable value_of_the_variable\" for example : #define PI 3.14159" << std::endl; std::cout << "Then we can use the variable PI : for example : std::cout << PI << std::endl will output :" << PI << std::endl << std::endl; std::cout << "Notice that they are special constant in C++ like __LINE__, __FILE__, __DATE__ or __TIME__ and much others, for example we can say :" << std::endl; std::cout << "This is the line number " << __LINE__; std::cout << " in the file " << __FILE__ << "." << std::endl; std::cout << "Today we are " << __DATE__; std::cout << " and it is " << __TIME__ << "." << std::endl << std::endl; std::cout << "You can also use the #define command to create macro. Macro is like a function that take arguments in parameter the syntax is the same : \"#define function(x) expression_with_x\"" << std::endl; std::cout << "But be aware they may be some error that are not errors for example we may think that the #define square1(x) x*x is going to return the square of x but that's wrong, in fact the parameter x will be replace in the expression like that :" << std::endl; std::cout << "square1(1+2) = 1+2*1+2 = 1+2+2=" << square1 (1+2) << std::endl; std::cout << "So a good correction will be : #define square2(x) ((x)*(x)), in fact : " << std::endl; std::cout << "square2(1+2) = ((1+2)*(1+2)) = (3*3)="<(b)?(a):(b))" << std::endl; std::cout << "And here we have max(1,2) = " << max(1,2) << std::endl; return 0; } #endif

playing with preprocessor